1. Technical Field
The present invention generally relates to ultrasound systems, and more particularly to an ultrasound system and a method for reducing noise and compensating aliasing in a Doppler mode image.
2. Background Art
An ultrasound system has become an important and popular diagnostic tool since it has a wide range of applications. Specifically, due to its non-invasive and non-destructive nature, the ultrasound has been extensively used in the medical fields. Modern high-performance ultrasound diagnostic systems and techniques are commonly used to produce two or three-dimensional diagnostic images of internal features of an object (e.g., human organs).
Generally, the ultrasound system may provide a brightness (B) mode for displaying a 2-dimensional image based on reflection coefficients of ultrasound signals in a target object, a Doppler mode for displaying an image of a moving object (e.g., blood flow) by using a Doppler effect, and an elasticity mode for displaying an image of a target object based on displacements of the target object before and after applying compression. In the Doppler mode, a Doppler mode image may be formed by using a frequency change (hereinafter, referred to as “Doppler frequency”) between a frequency of an ultrasound signal transmitted from a probe hereinafter, referred to as “transmit frequency”) at a pulse repetition frequency (PRF) and a frequency of a Doppler signal reflected from a moving object (hereinafter, referred to as “receive frequency”). The Doppler mode image may be formed based on the characteristics in which the receive frequency for the target object moving toward the probe is higher than the transmit frequency and the receive frequency for the target object moving away from the probe is lower than the transmit frequency.
When the Doppler frequency is higher than ±PRF/2 in the Doppler mode, aliasing may occur. Thus, a high Doppler frequency may be misinterpreted as a low Doppler frequency and vice versa. As such, a direction of the blood flow may be incorrectly identified. Various methods for compensating for the aliasing have been introduced in the art. However, the conventional methods may compensate for the aliasing without considering noise in the Doppler signal. Accordingly, since the Doppler frequency may fluctuate between ±PRF/2 in approaching PRF/2 due to noise, detection and compensation of the aliasing may not be correctly carried out.